In response to recent outstanding developments in computers and like apparatuses, a new technology has been developed as a means for visualizing output information from those apparatuses, wherein ink in a mist state is sprayed so as to adhere onto a sheet of recording paper, thereby allowing letters and pictures to be recorded thereon. Ink jet printers using this technology provide a low noise printer that enables recording on ordinary paper as well as color printing.
Among the ink jet heads used in such ink jet printers, the thermal type is known. FIG. 16 shows the ink head main body 501 of the ink jet head of the thermal type. A nozzle 503 is fixed to one end of the ink head main body 501. The top portion of the nozzle 503 is connected to an orifice 502, and the other end of the nozzle 503 is connected to an ink storage section 505. An ink supply section, not shown, is connected to the ink storage section 505 through an ink inlet 504, and ink is supplied from the ink supply section through the ink inlet 504. A heater section 506 is installed in the proximity of the nozzle 503, and ink inside the ink storage section 505 is heated by the heater section 506 to vaporize abruptly. The resulting vapor pressure thus produced allows ink particles to be sprayed from the orifice 502.
In this method, however, it is necessary to heat the heater section 506 instantaneously to a high temperature in the vicinity of 1000.degree. C. upon spraying the ink particles; this results in a problem in the life of the heater section 506.
In order to solve this problem and to provide an ink jet head having a long life, a piezoelectric type has been developed. The ink jet head of this type is provided with a piezoelectric device 507, shown in FIG. 17, which mechanically oscillates in response to electric signals. In the ink jet head of this type, the ink jet head main body 510 has an orifice 502, and a piezoelectric device 507 is installed in an ink storage section 508 that connects the orifice 502 and the ink inlet 504. When the piezoelectric device 507 is driven, the volume of the ink storage section 508 is decreased, thereby increasing the pressure inside the ink storage section 508. This high pressure is applied to ink 509, thereby forcing ink particles 509a to be sprayed from the orifice 502.
In order to design a compact ink jet head having a high degree of integration, it is possible to achieve the objective by employing a well established, fine machining technique such as the etching method and other methods, if other conditions permit the application of the technique. In the above arrangement, however, the spraying force of the ink 509a is obtained through the mechanism wherein upon spraying ink, the volume of the ink storage section 508 is decreased to a size as small as the volume of the ink particles 509a. Therefore, it is necessary to provide a piezoelectric device 507 which is bigger than a predetermined size. This makes it difficult to design a compact ink jet head having a high degree of integration.
Moreover, the ink particles 509a are sprayed by the increased inner pressure of the ink storage section 508; therefore, once air (bubbles) enters the ink storage section 508, the bubbles are only pressurized by the driving operation of the piezoelectric device 507 even if the volume of the ink storage section 508 is decreased. This results in insufficient pressure to be applied to the ink 509, causing a problem in reliability due to difficulty in spraying the ink 509.
Japanese Laid-Open Patent Application No. 269058/1990 (Tokukaihei 2-269058) discloses a liquid-spraying apparatus wherein a force exerted by progressive waves is utilized. The apparatus is provided with, for example, tandem-type electrodes and reflectors that are installed on a substrate. Progressive waves occur in response to electric signals sent to the substrate from the tandem-type electrodes, and when liquid is imposed on the progressive waves, part of the liquid becomes mist and flies.
However, since the above liquid-spraying apparatus has a complicated structure, it cannot be produced by a batch process that uses the etching method or other methods. Consequently, it is difficult to make the apparatus compact, and the production cost of the apparatus is expensive.
Further, in order to spray the liquid in an appropriate direction, for each operation, it is necessary to provide preparatory work for accurately adjusting various factors such as frequency and voltage in ac electric signals, frequency and its duty ratio in pulse signals, angles made between the reflector and the substrate, etc. in accordance with the quantity and characteristics of the liquid.